I got a 6 volt motor working yesterday. Took it all apart and fixed the broken rivets and wire. The motor works great, but I am surprised at how many stock switches I have that are bad, NOT having to do with the resistor!
Anyway, all of the testing information is here:
http://devestechnet.com/Home/Native12VUpgrade#heatersystemNew content is in the big yellow box. I was getting about 240 degrees on the Reducer, but 350 degrees on the resistor on the switch. If I move the switch out of the reducer's influence and put it IGNITION-SWITCH-REDUCER-MOTOR, I got another 100 degrees on the already under-rated resistors. I shut that test down real fast. When you hear people complaining about how hot those resistors are, that at least points to the answer.